1. Field of the Invention
The present invention pertains to a method of etching a silicon-containing dielectric material. In particular, the invention pertains to a method of pattern etching a layer of a silicon-containing dielectric material for use as a hard mask during subsequent pattern etching of semiconductor device features having a feature size of about 0.15 μm or less.
2. Brief Description of the Background Art
Silicon-containing dielectric materials (such as silicon nitride, silicon oxide, and silicon oxynitride) are often used as hard masks for pattern etching of underlying layers in a semiconductor structure. The silicon-containing dielectric layer itself is typically patterned using an overlying, patterned photoresist. Selectivity for etching the silicon-containing dielectric layer relative to an overlying, organic photoresist is important during the hard mask patterning step. As used herein, the term “selectivity” or “etch selectivity” refers to a ratio of the etch rate of a first material (e.g., a silicon-containing dielectric material) to the etch rate of a second material (e.g., photoresist) using a given plasma source gas and processing conditions.
Conventional plasma etch processes for pattern etching silicon-containing dielectric materials utilize a source gas which is a combination of CF4 and CH2F2. While this etch chemistry typically provides good (at least 1.5:1) selectivity for etching the silicon-containing dielectric layer relative to the overlying photoresist, the resulting etch profile of a trench into the silicon-containing dielectric layer is typically tapered, as shown in FIG. 2A. Because the silicon-containing dielectric layer will be used as a hard mask for subsequent pattern etching of underlying material layers, it is important that the patterned etch profile of the silicon-containing dielectric layer exhibit an etched line sidewall angle, with respect to a horizontal base, which is as close to 90° as possible (typically ranging between about 88° and 92°). Any deviation from a substantially 90° etch profile will be reflected in the etch profiles of the underlying layers.